At times, these elements can work against one another. For example, if police make full-blown custodial arrests of all offenders, they risk reducing the police presence in the target area when they leave it to book prisoners. Or publicity about a crackdown in a target area might cause offenders simply to avoid that area and commit crimes elsewhere.

Several researchers have asserted that the best way to maximize the benefits of crackdowns is to conduct them briefly and intensively, rotate them among several target areas, and resume them either at unpredictable times in the future or when target offenses return to certain predetermined levels.7

For crackdowns to be effective, they must be sufficiently strong and long: strong enough doses of police intervention for long enough periods. Marginal increases in routine police activity are unlikely to produce significant effects. Exactly how much more intensive and extensive police action is required varies from problem to problem, but it must be sufficiently greater than normal to alter offenders' perceptions of risk.† If a crackdown is spread too thinly over too wide an area, its overall intensity may be insufficient to have much of an effect. Follow-up crackdowns to reinforce an initial crackdown typically do not need to be as intense.

† You may need to make special efforts to inform potential offenders about the heightened risks of apprehension: do not assume they obtain or process information about police activity in the same way as the general public might. One of the keys to effective deterrence in the Boston Gun Violence Project was how officials personally and persuasively told high-risk offenders about the new consequences for violent acts (Kennedy et al. 2001). [Full text]

An Effective Drug Crackdown in San Diego

San Diego police were witnessing a full-blown crack epidemic on University Avenue . Heavily populated with seasoned and hard-core drug users, the street remained an entrenched drug market, stabilized by word-of-mouth marketing.

Applying basic marketing principles to both the illegal drug market and the legitimate retail merchandise market, police convinced drug users that University Avenue was the last place they wanted to be, and helped businesses convince residents that it was a convenient and safe place to shop. They divided their response into three stages: Operation Hot Pipe, Operation Smoky Haze, and Operation Rehab.

Operation Hot Pipe's goal was to destroy the perception that University Avenue was a safe and suitable environment for crack users. Officers established the area as a high-intensity zone and warned drug users that they would arrest them for any and all crimes committed there. Squads of officers began to systematically arrest drug users who loitered on University Avenue and who facilitated the drug market. Police identified three types of crack users: habitual users-facilitators, binge users, and partyers (who came to buy crack and then went home). The bingers and partyers depended on the habitual users for drugs. Police reasoned that if that group disappeared, the bingers and partyers would have to look elsewhere.

Officers told arrestees they would focus enforcement on them as long as they stayed in the target area, and gave them fliers designating University Avenue as off-limits to crack users. At first, the users did not believe officers, but it did not take long before the habitual ones began offering information to avoid arrest; officers arrested them anyway. One user walked into jail and was handed a flier, and as the arresting officers left, they heard the prisoner reading the flier to other inmates. Police also posted fliers on storefronts, on electrical boxes, on planters, on windows, at bus stops, and in places identified as drug-dealing sites. Police told each person contacted to tell his or her friends that University Avenue was too hot to hang out.

Operation Smoky Haze's goal was to destroy the drug market's convenience and safety by confusing the buyers and sellers. Officers used an undercover, reverse-sting operation, arresting buyers for solicitation. Buyers became leery of fresh faces selling on University Avenue . Officers used informants to spread the word that the operation was continuing. They also casually leaked information to users about pending drug sweeps–some of which occurred, and some of which did not. They spread the word that dealers were ripping off buyers. During field interviews, they asked users for information concerning drug rip-offs and robberies, or for information on phantom suspects. The resulting confusion made buying inconvenient and risky. Officers also referred people to a newly formed drug court. Those who applied and were eligible were put on drug court probation.

Operation Rehab's goal was to change people's perception of the area from that of a drug corridor to that of a strong business community, through an intense positive marketing campaign.

As a result of the initiative, merchants reported that business had increased, they felt safer on University Avenue , and they were seeing more families and shoppers on the street. The habitual users became aware of increased enforcement through their own or acquaintances' arrests and the fliers. They reported that crack was harder to find. Some users left the area altogether. Street robberies declined. And complaints about drug dealing all but ceased.